Because there are more than 65,535 characters. That's just writing systems, not Unicode's fault. Most of the unnecessary complexity of Unicode is legacy compatibility: UTF-16 & UTF-32 are bad ideas that increase complexity, but they predate UTF-8 which actually works decently well so they get kept around for backwards compatibility. Likewise with the need for multiple normalization forms.
So, seeing this just moved the complexity of Unicode one notch up in my head, and I respect the guys who designed and made it work. It was not whining or complaining of any sort. :)
It takes up to eight bytes per character in Unicode if you want to support both Chinese and Japanese in a single font using IVS(and I don't think there's any font that actually supports this).
AFAICS(As far as I can search), Simplified(PRC) and Traditional(Taiwan) Chinese encoding are respectively called GB2312 and Big5, and they're both two byte encodings with good practical coverage. Same applies for Japanese Shift_JIS. If e.g. :flag_cc: were allowed to be used as start-of-language marker, one could theoretically cut that back down to two bytes per character without losing much and actually improving language supports.
FYI, it's never S. If there is no better option then SS and ss are the proper capital and lowercase substitutions.
...but it's a complex operation. This is what libICU is mostly for. You can't just look-up a single table and convert a string to another like you work on ASCII table or any other simple encoding.
Germans have their ß to S (or capital ß depending on the year), Turkish has ı/I and i/İ pairs, and tons of other languages have other rules.
Esp, this I/ı and İ/i pairs break tons of applications in very unexpected ways. I don't remember how many bugs I reported, and how many workarounds I have implemented in my systems.
Adding a type is nice, but the surrounding machinery is so big, it brings tons of work with itself. Unicode is such a complicated system, that I read that even you need two UTF-16 characters (4 bytes in total) to encode a single character. This is insane (as in complexity, I guess they have their reasons).